[REVIEW] WCC performance/memory footprint optimization

[seunghwak]

• Performance tune/reduce memory footprint for WCC for SG & MG (when # GPUs < (E/V)^2, additional memory footprint optimizations are necessary if # GPUs > (E/V)^2 and this will be addressed in separate PRs).
• MG bug fixes

[codecov-commenter]

Codecov Report

❗ No coverage uploaded for pull request base (branch-21.06@ad92c1e). Click here to learn what that means.
The diff coverage is n/a.

@@               Coverage Diff               @@
##             branch-21.06    #1605   +/-   ##
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  Coverage                ?   59.10%           
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  Files                   ?       79           
  Lines                   ?     3482           
  Branches                ?        0           
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  Hits                    ?     2058           
  Misses                  ?     1424           
  Partials                ?        0           

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[BradReesWork]

@gpucibot merge